How many calories do you actually need per day?

Pair of woman's hands holding cutlery eating a fresh healthy raw spring salad with butternut pumpkin squash at a casual outdoor dining meal location (warrengoldswain)

Nutrition terms like “calories” are thrown around all the time, and you see them come up on nutrition labels and in conversation. How exactly do calories relate to your health and weight, and what do you need to know about them?

First of all, what exactly is a calorie?
A calorie is a unit of energy used to measure energy in (calories from food and drink) and energy out (calories burned through basic bodily functions like breathing, as well as from physical activity).

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How many calories do you need?
Your calorie needs depend on your weight, height, age, gender, activity level, and other factors (like pregnancy). “If you exercise on a regular basis, you will need to take in a bit more calories to maintain your weight,” Alissa Rumsey, MS, RD, a dietitian in New York City, told Fox News. “However, exercise doesn't burn quite as much as we think, and it is not possible to exercise away an overly caloric diet.”

Many online calculators exist — and in the scientific community, Mifflin St. Jeor and Harris-Benedict and are viewed as two of the most accurate. “These equations calculate the number of calories your body needs to function while at rest,” explained Angie Asche, MS, RD, a sports nutritionist and owner of Eleat Sports Nutrition. While calorie needs vary greatly by person, women tend to need 1,600 to 2,400 calories per day, and men typically require between 2,000 and 3,000. Of course, there are many instances in which someone might require more or less, and you can find a registered dietitian in your area at eatright.org to help you determine individual needs.

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You don’t necessarily need to count calories, though. Many nutrition experts are proponents of mindful eating, which encourages tuning in and listening to the cues that tell you when you’re hungry and when you’re beginning to feel full.  “Balance your plate with meals made of mostly whole foods, including plenty of protein, healthy fats, and fiber,” Rumsey said. “By doing this, you will naturally consume fewer calories because you'll feel full and satiated.”

Does the quality of calories matter?
“Nutrient density is a concept that is just as important, if not more so, than calories,” Rumsey told Fox News. Think about eating 100 calories worth of potato chips versus almonds. “While they both contain the same number of calories, the almonds provide protein, healthy fats, fiber, vitamins, minerals, and antioxidants — and the potato chips are just carbs and some salt,” Rumsey said. Because the nutrients that the foods contain are so different, your body will treat them as such. You’ll absorb the almonds more slowly, helping to stabilize your blood sugar and keep you fuller for longer. You’ll burn through the potato chips more quickly, perhaps wanting to eat more as a result.

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How do calories relate to weight loss and weight gain?
While one pound equates to 3,500 calories, weight loss and weight gain aren’t as simple as calories in and calories out. But let’s start here: If you want to lose weight, you’ll need a deficit so you’re burning more than you’re taking in.

Avoid eating too few calories, though. “A calorie deficit that’s too low sets you up for failure,” Asche said. “It can put your body in starvation mode, slowing your metabolism and resulting in lean muscle mass loss.” You’ll see many quick-fix diets advocating 1,200 calories or less, but these can be detrimental to your metabolism when followed long term. “Something like a cleanse or detox is going to result in you losing straight water weight, anyway,” Asche said. Translation: Much of the “fast” weight loss is weight you may gain back once you go back to eating a normal diet. Instead of a speedy weight loss, aim for a slower, lasting one, with a goal of losing 1 to 2 pounds per week. This is typically an average loss over time because your body isn’t a machine — you’re likely to lose a little more one week, a little less another. Aim for a deficit of 500 to 1,000 calories daily, which you can accomplish through a combination of reducing calories and increasing exercise.

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To lose weight without feeling hungry, you’ll want to add volume in the form of fruits and vegetables, since the water and fiber they contain helps you feel satiated — as well as whole grains, providing fiber and protein. Look first to cutting calories from added sugar, which doesn’t provide a nutritional benefit. Once you’ve reached your goal, it will be important to continue with regular physical activity. “Research shows this is important in order to maintain that weight loss,” Rumsey said.

Looking to gain weight? Focus on eating more nutritious foods that are higher in calories, like nuts, seeds and avocado.

Amy Gorin is freelance writer and owner of Amy Gorin Nutrition in Jersey City, NJ. Connect with her on Facebook, Instagram, Twitter, and Pinterest.